The present invention relates to scalpel blades and particularly to ultrasonically applied surgical scalpel blades having improved cutting and coagulation efficiency, and methods of applying the blades to a substrate for cutting.
From the advent of surgery, various types of surgical instruments for incising and dissecting human and animal tissue have been employed. It has long been a tenet of surgical procedures that the sharper the blade, the more efficient the cutting action. More modern techniques for incising and dissecting include electrosurgical cutting, which has the added benefit of affording coagulation simultaneous with the cutting. Thus, cutting with moderate or significant hemostasis can be achieved using electrosurgical techniques. Concomitantly, however, electrosurgical techniques cause significant thermal injury to tissues as a by-product of coagulation.
More recently, however, ultrasonic surgical devices for performing surgical procedures have been developed, for example, as disclosed in the above-identified applications. Generally speaking, these surgical devices are hand-held instruments connected to a source of ultrasonic energy. The ultrasonic energy is transmitted through a connection or mount between the ultrasonic energy source and a hand-held coupler which mounts the surgical tool, for example, a surgical blade mounted at the tip of the coupler. This facilitates transmission of ultrasonic energy from the ultrasonic energy source through the coupler to the surgical blade to generate ultrasonic vibrations in the blade. Until the present invention, however, the mechanism of the interaction of the vibrating blade and the adjoining tissue was not sufficiently well understood in relation to cutting and coagulation and generally it was thought that the same sharp blades used in hand-held surgical scalpels should be applied to ultrasonic surgical scalpels.
According to the present invention, it has been discovered that in ultrasonic surgical instruments of this type, coagulation is achieved while cutting by reducing the sharpness and hence increasing the dullness or bluntness of the blade in comparison with standard sharp blades. It is possible to achieve a perceived sharpness corresponding to the sharpness provided by the mechanical configuration of the sharp blade edges of standard scalpels while simultaneously achieving coagulation in the various tissues. That is to say, it has been discovered that the application of ultrasonic power to an otherwise dull blade enhances the sharpness of the blade when applied to incise and dissect and achieves simultaneous coagulation. This has been discovered by an improved understanding of the interaction of the vibrating blade and various tissues.
Heat is produced in tissue as ultrasonic blade motion couples with the tissue, the tissue moving with the blade surface. The mechanical energy within the tissue is converted to heat as a result of the friction and shear stress within the tissue which breaks chemical bonds that give the protein structure. The heat and mechanical energy cause the highly structured protein, i.e., collagen and muscle protein, to denature, i.e., become less organized, into a white coagulum. Coagulation is a function of the blade velocity, the extent of blade and tissue coupling and the duration of the contact between the blade and the tissue. Blade velocity is a function of ultrasonic frequency and amplitude or displacement per cycle. Thus, at constant frequency, displacement is a function of the electrical power input to the transducer. Coupling of the blade motion to the tissue requires adequate force between the blade and tissue, friction and surface area. The blade surfaces may not, therefore, be lubricious. To the contrary, high friction coefficients of blade material are therefore desirable.
With respect to cutting and coagulation, the magnitude of the heat produced is inversely proportional to the blade sharpness and incision or dissection speed. Sharp blades pass through the tissue with less force and less tissue coupling, hence less coagulation is produced. Thus, in order to achieve tissue coagulation and hemostasis, ultrasonic scalpel blades cannot be as sharp as surgical scalpel blades; furthermore, ultrasonic scalpel blades do not need to be as sharp as standard scalpel blades because the ultrasonic motion enhances the sharpness and the cutting is perceived to be as sharp or sharper than standard scalpel blades. The ultrasonic motion essentially compensates for the reduced sharpness of the blade. That advantage affords another benefit in that substantial heat and mechanical energy input to the tissue enables coagulation.
This discovery of the mechanism of cutting and coagulation with ultrasonic scalpel blades not only has led to the conclusion that relatively dull blades should be utilized in ultrasonic scalpel applications but also that the degree of sharpness or dullness of the blade edge affects coagulation in different tissue. For example, in skin and muscle tissue with high protein content, a relatively sharp blade may efficiently cut through the skin and muscle with minimum heat generation and mechanical coupling to the tissue because of the protein-rich environment which more readily produces the white coagulum necessary to seal a blood vessel. However, in less dense tissue, such as fat, fascia and parenchyma, where little collagen or protein is available to facilitate coagulation of bleeders during incisions, a less sharp or more dull blade is used. During ultrasonic motion of the blade through the collagen or protein-poor tissue, the blade will coapt the blood vessel before cutting through it with sufficient mechanical energy generated to form the coagulum necessary to attain hemostasis. Furthermore, effective cutting in less dense tissues can be achieved with very dull ultrasonic scalpel blades as these tissues are generally easier to cut.
The application of ultrasonic energy to scalpel blades in different tissues and conditions of surgery has required development of a variety of blades and blade edge geometries to achieve the necessary sharpness or dullness, depending upon the application.
In accordance with the present invention, it has been found that increasing the angle of the blade edge faces causes (i) the reduction in sharpness necessary to improve the coupling of ultrasonic motion with the tissues and (ii) blood vessel compression during cutting. It has been found that applying ultrasonic energy to a typically sharp scalpel blade results in virtually little or no coagulation.
It has also been found that because of the different tissues through which incisions or dissections are made, different blade edges having different included angles are desirable for ultrasonically actuated blades. These can be provided in blades having different included angles or a single blade having discrete blade edges with different included angles and hence different dullness or sharpness. With respect to the sharpness of the blade, typically a sharp scalpel of conventional design and used manually has an included blade edge face angle of 22.degree. and, as noted previously, the trend has been toward ever-increasing sharpness of that blade with smaller included angles. In accordance with the present invention, however, an included blade edge face angle of 25.degree.-50.degree. has been found satisfactory, with a perceived sharpness corresponding to the sharpness of a typical blade having a blade edge of approximately 22.degree.. Also, the various and different tissues to be incised to a large extent optimally determine the degree of dullness of the blade. For example, a blade edge face angle of about 25.degree. with a hard sharpenable edge of NiCr alloy or beta titanium may achieve hemostasis in dermatologic, plastic and opthalmic surgery, with very slow cutting. The degree of perceived sharpness is greater or equal to an extremely sharp standard, manually applied, scalpel blade. For cutting tissue with high protein concentration, for example, skin and muscle, with average sharpness and excellent hemortasis, a blade edge face angle of between 30.degree.-40.degree. using a nickel chrome or beta titanium alloy coating on the edge may be employed. While a blade of this type may also cut fat, fascia, connective tissue and parenchyma with excellent sharpness, it does not readily cut highly elastic dense structures such as large blood vessels, nerves and outer linings of many structures of the alimentary canal, urogenital system and the gall bladder. A blade of this type, however, is ideal for endoscopic surgery.
For cutting skin and muscle with fair sharpness, a blade edge face angle of 40.degree.-50.degree. with a nickel chrome or beta titanium alloy coating may be used. This blade edge can be used to dissect through fat with good hemostasis and solid parenchymas tissue with fair hemostasis during fat and fascia plane dissection.
A blade formed entirely of aluminum or titanium without a coated edge and having a blade edge face angle of 25.degree.-45.degree. provides hemostatic blunt dissection in fat and through tissue planes between skin and fat and fat and fascia. Blood vessels up to three millimeters may be coagulated during these dissections.
Blade edge design may thus be optimized for procedures where only one tissue type is incised. That is, a particular blade edge face angle for a particular tissue is provided for optimizing cutting and coagulation. However, where two or more tissues are to be incised, dual-edge blades may overcome the deficiencies of a blade optimized for only one type of tissue. Hence, in accordance with the present invention, a blade having one section formed to have an included blade edge face angle, for example, on the order of about 25.degree.-35.degree. and another section having a different included blade edge face angle, for example, on the order of 25.degree.-45.degree., may be provided. Consequently, the one blade section may be used for incision of one tissue type, while the other blade section may be used for the incision of another tissue type. A variable edge may also be provided. For example, to cut full skin thickness in the scalp and forehead with hemostasis, a variable blade edge that is sharp, i.e., about 25.degree.-35.degree. on a straight section and through one-half of the radius and less sharp, i.e., more dull (45.degree. or more or formed of aluminum), through the remainder of the radius and tip is effective for full skin thickness scalp incisions. The dull tip can penetrate the skin when ultrasonically activated since the skin is supported and backed by the skull bone. The sharp blade edge on the straight section cuts the skin with ease and is hemostatic because of the high collagen concentration in the skin. The blunt tip and radius cuts and coagulates the extensive subcutaneous vascular plexus that lies beneath the skin in the thin subcutaneous fat layer. The relatively blunt edge near and at the tip compresses the vascular plexus against the skull bone and seals the vessels as they are cut.
Full thickness skin incisions using a blade edge having an included blade edge face angle of 20.degree.-40.degree. is very hemostatic in the skin. However, should the incision extend into fat, some bleeding is encountered. By rounding the blade tip, coagulation in the deep dermis and fat is improved. The curved tip is also ideal for endoscopic applications because it reduces the risk of accidentally puncturing internal structures.
In a preferred embodiment according to the present invention, there is provided a blade for an ultrasonic scalpel having a cutting edge defined by a pair of cutting edge faces having an included angle of at least about 25.degree. whereby a perceptively sharper blade and coagulation of the blood vessels in the incision upon application of ultrasonic power to the blade are obtained.
In a further preferred embodiment according to the present invention, there is provided a method of incising tissue comprising the steps of selecting an ultrasonically actuated scalpel blade from a plurality of blades each having different included and increasing blade angles of at least about 25.degree. in inverse proportion to the protein content of the tissue to be incised and applying energy to the selected blades to ultrasonically vibrate the blades thereby to achieve substantially simultaneous cutting with perceived enhanced sharpness and hemostasis.
In a still further preferred embodiment according to the present invention, there is provided a method of incising different tissues employing a single scalpel blade comprising the steps of providing an ultrasonically actuated scalpel blade having at least two discrete edge portions with different included angles, both being at least 25.degree., applying one of the discrete edge portions to one of the tissues to dissect the one tissue, applying energy to the blade to ultrasonically vibrate the blade to achieve cutting and hemostasis of the one tissue, applying the other edge portion to the other of the tissues and applying energy to the blade to ultrasonically vibrate the blade when the other edge portion is applied to the other tissue to achieve simultaneous cutting and hemostasis in the other tissue.
In a still further preferred embodiment according to the present invention, there is provided a method of incising tissue comprising the steps of selecting an ultrasonically activated blade from a plurality of blades each having different included and increasing blade angles thereby affording blades that are less than surgically sharp and having a bluntness and dullness in inverse proportion to the protein content of the tissues to be incised and applying energy to the selected blades to ultrasonically vibrate the blade thereby to achieve tissue coagulation and hemostasis and simultaneously achieve a cutting sharpness that is perceived to be at least equivalent to the sharpness of standard surgical blades.
Accordingly, it is a primary object of the present invention to provide a novel and improved ultrasonic actuated scalpel blade having improved cutting and coagulation characteristics.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings